1. Field of the Invention
The present invention relates to a front derailleur for bicycle use. More particularly, the present invention relates to a front derailleur configured to be mounted to the frame of a bicycle by a fastening piece.
2. Background Information
There are front derailleurs for bicycles that are mounted to the bicycle frame with a fastening piece that is disposed between the front derailleur and the bicycle frame. The fastening piece used with this kind of front derailleur has a fixing part that is fixed to the frame by welding or the like and a support part configured to support the front derailleur. Since the position to which the fastening piece is installed on the frame depends on the quality of the work performed when fixing the fixing part to the frame, there are times when the installation precision of the fastening piece is poor. When the installation precision of the fastening piece (more specifically, the fixing part) is poor, the position of the support part is offset from where it should be and, consequently, there are cases in which the front derailleur cannot be installed in the prescribed position. For example, if the fastening piece is installed poorly on the seat tube of the bicycle frame, the support part might be out of position relative to the circumferential direction of the seat tube or in the lengthwise direction of the seat tube.
In order to resolve this issue, a front bicycle derailleur has been proposed in U.S. Pat. No. 4,199,997 (Japanese Laid-Open Patent Publication 53-102550), assigned to Shimano Inc., that is mounted to a support part in such a manner that it can be swung about a center axis of the seat tube and moved up and down along the lengthwise direction of the seat tube in order to adjust the mounting position. The front derailleur basically includes a chain guide, a four bar-linkage mechanism, and a front derailleur main body having a fastening piece with a mounting part configured to be mounted to the support part by a fastening screw. The structure of the front derailleur and the fastening piece presented in the publication will now be described in further detail.
The support part has a first curved support face that is curved in such a manner as to have the shape of a circular arc in a cross sectional view of the support part lying in a plane normal to the lengthwise direction of the seat tube and a first through hole that runs through the first curved support face substantially in a second direction perpendicular to the lengthwise direction of the seat tube. The first through hole is elongated in a direction substantially parallel to the lengthwise direction of the seat tube.
The mounting part has a mounting face that is curved in a manner corresponding to the contour of the first curved support face of the support part in a cross sectional view of the support part lying in a plane normal to the lengthwise direction of the seat tube. The mounting part of the front derailleur main body is mounted to the support part with the fastening screw that passes through the first through hole of the support part in such a manner as to extend in a direction substantially parallel to the second direction.
Since the first through hole of the support part of the fastening piece is elongated in a direction substantially parallel to the lengthwise direction of the seat tube, the mounting part of the front derailleur main body can be moved along a path substantially parallel to the lengthwise direction of the seat tube with respect to the support part when the mounting part is being mounted to the support part. Additionally, since the first curved support face is curved in such a manner as to have the shape of a circular arc in a cross sectional view of the support part lying in a plane normal to the lengthwise direction of the seat tube and the mounting face is curved in a manner corresponding to the contour of the first curved support face of the support part in a cross sectional view of the mounting part lying in a plane normal to the lengthwise direction of the seat tube, the front derailleur main body can be swung about the center of curvature of the first curved support face (i.e., its position can be adjusted in a manner that approximates turning about the center axis of the seat tube) when the mounting part is being mounted to the support part.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved front derailleur. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.